Auto merge of #140549 - BoxyUwU:proper_const_norm, r=lcnr

Set groundwork for proper const normalization

r? lcnr

Updates a lot of our normalization/alias infrastructure to be setup to handle mgca aliases and normalization once const items are represented more like aliases than bodies. Inherent associated consts are still super busted, I didn't update the assertions that IACs the right arg setup because that winds up being somewhat involved to do *before* proper support for normalizing const aliases is implemented.

I dont *intend* for this to have any effect on stable. We continue normalizing via ctfe on stable and the codepaths in `project` for consts should only be reachable with mgca or ace.

Author: bors

compiler/rustc_infer/src/infer/projection.rs

@@ -1,7 +1,8 @@
 use rustc_middle::traits::ObligationCause;
-use rustc_middle::ty::{self, Ty};
+use rustc_middle::ty;
 
 use super::InferCtxt;
+use crate::infer::Term;
 use crate::traits::{Obligation, PredicateObligations};
 
 impl<'tcx> InferCtxt<'tcx> {
@@ -11,24 +12,32 @@ impl<'tcx> InferCtxt<'tcx> {
     /// of the given projection. This allows us to proceed with projections
     /// while they cannot be resolved yet due to missing information or
     /// simply due to the lack of access to the trait resolution machinery.
-    pub fn projection_ty_to_infer(
+    pub fn projection_term_to_infer(
         &self,
         param_env: ty::ParamEnv<'tcx>,
-        projection_ty: ty::AliasTy<'tcx>,
+        alias_term: ty::AliasTerm<'tcx>,
         cause: ObligationCause<'tcx>,
         recursion_depth: usize,
         obligations: &mut PredicateObligations<'tcx>,
-    ) -> Ty<'tcx> {
+    ) -> Term<'tcx> {
         debug_assert!(!self.next_trait_solver());
-        let ty_var = self.next_ty_var(self.tcx.def_span(projection_ty.def_id));
+
+        let span = self.tcx.def_span(alias_term.def_id);
+        let infer_var = if alias_term.kind(self.tcx).is_type() {
+            self.next_ty_var(span).into()
+        } else {
+            self.next_const_var(span).into()
+        };
+
         let projection =
             ty::PredicateKind::Clause(ty::ClauseKind::Projection(ty::ProjectionPredicate {
-                projection_term: projection_ty.into(),
-                term: ty_var.into(),
+                projection_term: alias_term,
+                term: infer_var,
             }));
         let obligation =
             Obligation::with_depth(self.tcx, cause, recursion_depth, param_env, projection);
         obligations.push(obligation);
-        ty_var
+
+        infer_var
     }
 }

compiler/rustc_middle/src/ty/context.rs

@@ -243,10 +243,18 @@ impl<'tcx> Interner for TyCtxt<'tcx> {
                     ty::AliasTermKind::ProjectionTy
                 }
             }
+            DefKind::AssocConst => {
+                if let DefKind::Impl { of_trait: false } = self.def_kind(self.parent(alias.def_id))
+                {
+                    ty::AliasTermKind::InherentConst
+                } else {
+                    ty::AliasTermKind::ProjectionConst
+                }
+            }
             DefKind::OpaqueTy => ty::AliasTermKind::OpaqueTy,
             DefKind::TyAlias => ty::AliasTermKind::FreeTy,
-            DefKind::AssocConst => ty::AliasTermKind::ProjectionConst,
-            DefKind::AnonConst | DefKind::Const | DefKind::Ctor(_, CtorKind::Const) => {
+            DefKind::Const => ty::AliasTermKind::FreeConst,
+            DefKind::AnonConst | DefKind::Ctor(_, CtorKind::Const) => {
                 ty::AliasTermKind::UnevaluatedConst
             }
             kind => bug!("unexpected DefKind in AliasTy: {kind:?}"),

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -3195,7 +3195,7 @@ define_print! {
 
     ty::AliasTerm<'tcx> {
         match self.kind(cx.tcx()) {
-            ty::AliasTermKind::InherentTy => p!(pretty_print_inherent_projection(*self)),
+            ty::AliasTermKind::InherentTy | ty::AliasTermKind::InherentConst => p!(pretty_print_inherent_projection(*self)),
             ty::AliasTermKind::ProjectionTy => {
                 if !(cx.should_print_verbose() || with_reduced_queries())
                     && cx.tcx().is_impl_trait_in_trait(self.def_id)
@@ -3205,7 +3205,8 @@ define_print! {
                     p!(print_def_path(self.def_id, self.args));
                 }
             }
-            | ty::AliasTermKind::FreeTy
+            ty::AliasTermKind::FreeTy
+            | ty::AliasTermKind::FreeConst
             | ty::AliasTermKind::OpaqueTy
             | ty::AliasTermKind::UnevaluatedConst
             | ty::AliasTermKind::ProjectionConst => {

compiler/rustc_middle/src/ty/util.rs

@@ -966,7 +966,9 @@ impl<'tcx> TyCtxt<'tcx> {
             }
             ty::AliasTermKind::OpaqueTy => Some(self.variances_of(def_id)),
             ty::AliasTermKind::InherentTy
+            | ty::AliasTermKind::InherentConst
             | ty::AliasTermKind::FreeTy
+            | ty::AliasTermKind::FreeConst
             | ty::AliasTermKind::UnevaluatedConst
             | ty::AliasTermKind::ProjectionConst => None,
         }

compiler/rustc_mir_build/src/thir/pattern/mod.rs

@@ -567,6 +567,8 @@ impl<'a, 'tcx> PatCtxt<'a, 'tcx> {
 
         // Lower the named constant to a THIR pattern.
         let args = self.typeck_results.node_args(id);
+        // FIXME(mgca): we will need to special case IACs here to have type system compatible
+        // generic args, instead of how we represent them in body expressions.
         let c = ty::Const::new_unevaluated(self.tcx, ty::UnevaluatedConst { def: def_id, args });
         let mut pattern = self.const_to_pat(c, ty, id, span);
 

compiler/rustc_next_trait_solver/src/solve/normalizes_to/free_alias.rs

@@ -19,19 +19,25 @@ where
         goal: Goal<I, ty::NormalizesTo<I>>,
     ) -> QueryResult<I> {
         let cx = self.cx();
-        let free_ty = goal.predicate.alias;
+        let free_alias = goal.predicate.alias;
 
         // Check where clauses
         self.add_goals(
             GoalSource::Misc,
-            cx.predicates_of(free_ty.def_id)
-                .iter_instantiated(cx, free_ty.args)
+            cx.predicates_of(free_alias.def_id)
+                .iter_instantiated(cx, free_alias.args)
                 .map(|pred| goal.with(cx, pred)),
         );
 
-        let actual = cx.type_of(free_ty.def_id).instantiate(cx, free_ty.args);
-        self.instantiate_normalizes_to_term(goal, actual.into());
+        let actual = if free_alias.kind(cx).is_type() {
+            cx.type_of(free_alias.def_id).instantiate(cx, free_alias.args)
+        } else {
+            // FIXME(mgca): once const items are actual aliases defined as equal to type system consts
+            // this should instead return that.
+            panic!("normalizing free const aliases in the type system is unsupported");
+        };
 
+        self.instantiate_normalizes_to_term(goal, actual.into());
         self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
     }
 }

compiler/rustc_next_trait_solver/src/solve/normalizes_to/inherent.rs

@@ -15,12 +15,12 @@ where
     D: SolverDelegate<Interner = I>,
     I: Interner,
 {
-    pub(super) fn normalize_inherent_associated_type(
+    pub(super) fn normalize_inherent_associated_term(
         &mut self,
         goal: Goal<I, ty::NormalizesTo<I>>,
     ) -> QueryResult<I> {
         let cx = self.cx();
-        let inherent = goal.predicate.alias.expect_ty(cx);
+        let inherent = goal.predicate.alias;
 
         let impl_def_id = cx.parent(inherent.def_id);
         let impl_args = self.fresh_args_for_item(impl_def_id);
@@ -48,8 +48,13 @@ where
                 .map(|pred| goal.with(cx, pred)),
         );
 
-        let normalized = cx.type_of(inherent.def_id).instantiate(cx, inherent_args);
-        self.instantiate_normalizes_to_term(goal, normalized.into());
+        let normalized = if inherent.kind(cx).is_type() {
+            cx.type_of(inherent.def_id).instantiate(cx, inherent_args).into()
+        } else {
+            // FIXME(mgca): Properly handle IACs in the type system
+            panic!("normalizing inherent associated consts in the type system is unsupported");
+        };
+        self.instantiate_normalizes_to_term(goal, normalized);
         self.evaluate_added_goals_and_make_canonical_response(Certainty::Yes)
     }
 }

compiler/rustc_next_trait_solver/src/solve/normalizes_to/mod.rs

@@ -48,9 +48,13 @@ where
                     })
                 })
             }
-            ty::AliasTermKind::InherentTy => self.normalize_inherent_associated_type(goal),
+            ty::AliasTermKind::InherentTy | ty::AliasTermKind::InherentConst => {
+                self.normalize_inherent_associated_term(goal)
+            }
             ty::AliasTermKind::OpaqueTy => self.normalize_opaque_type(goal),
-            ty::AliasTermKind::FreeTy => self.normalize_free_alias(goal),
+            ty::AliasTermKind::FreeTy | ty::AliasTermKind::FreeConst => {
+                self.normalize_free_alias(goal)
+            }
             ty::AliasTermKind::UnevaluatedConst => self.normalize_anon_const(goal),
         }
     }
@@ -333,6 +337,8 @@ where
                     cx.type_of(target_item_def_id).map_bound(|ty| ty.into())
                 }
                 ty::AliasTermKind::ProjectionConst => {
+                    // FIXME(mgca): once const items are actual aliases defined as equal to type system consts
+                    // this should instead return that.
                     if cx.features().associated_const_equality() {
                         panic!("associated const projection is not supported yet")
                     } else {

compiler/rustc_trait_selection/src/traits/mod.rs

@@ -51,7 +51,7 @@ pub use self::dyn_compatibility::{
 pub use self::engine::{ObligationCtxt, TraitEngineExt};
 pub use self::fulfill::{FulfillmentContext, OldSolverError, PendingPredicateObligation};
 pub use self::normalize::NormalizeExt;
-pub use self::project::{normalize_inherent_projection, normalize_projection_ty};
+pub use self::project::{normalize_inherent_projection, normalize_projection_term};
 pub use self::select::{
     EvaluationCache, EvaluationResult, IntercrateAmbiguityCause, OverflowError, SelectionCache,
     SelectionContext,